[Zope] how do i make a python script ?

hello, i have this z-class with a text element and i'd like to parse this text before displaying it ? say, evrytime there is "zope" written in it i'd like to replace it on the fly with <b>zope</b>. i think the right direction to look at is a script (a pythonscript ?) that would be called as a method on this element. am i right or a i wrong ? what would the best starting point be ? thx $ven